But it’s now been revealed Network Rail first flagged up delays, some of which were caused by overhead wires being installed at the wrong height, on the £742 million project as far back as February.

At the time contractors thought they could make up the time and still hit the original deadline of December this year.

But in Holyrood last week, ScotRail boss Phil Verster revealed an updated programme was “advised to the minister come March/April” which “looked very different to the one we thought in February would be achievable”.

Transport Scotland last night said they were officially told of the seven-month delay by Network Rail on May 4.

Critics last night demanded to know why it took two months to share this information and why the SNP manifesto boasted the electrification would be completed by December this year.

Labour transport spokesman Neil Bibby said: “This is very serious. SNP ministers were advised of the delay before the election but said nothing.

“It looks right now like they planned to keep commuters in the dark for as long as possible and that simply isn’t good enough.”

As the Sunday Post revealed earlier this month, an extra £32m was spent on the Edinburgh to Glasgow Improvement Programme (EGIP) last year alone with the overall cost of the £742m scheme set to soar.

Rail regulators revealed part of the reason for the seven-month delay to the scheme was due to some of the route’s overhead wires and railway bridge walls being too low to meet vital safety standards.

Speaking to MSPs last week, Mr Verster said initially they thought they could make up the time lost but, “as we kept on digging and finding problems in this programme, we found more issues”.

He continued: “In the end, the programme which we then advised to the minister come March/April – that programme looked very different to the one we thought in February would be achievable and we started to share what we thought the cost estimates were.”

Current finance secretary Derek Mackay was transport minister until May 18 when his SNP colleague Humza Yousaf took over.

A Transport Scotland review of EGIP, being aided by private consultants Ernst and Young, is expected to report back next month and will reveal the latest cost of the scheme to slash journey times between Scotland’s biggest cities.

A Transport Scotland spokesman said: “In March this year Network Rail advised us of an eight-week delay to the EGIP electrification implementation programme, however at that point they maintained the entry into service date of December 2016 remained achievable.

“In early May, Network Rail told us that, based on their updated risk analysis, the entry into service date of December 2016 was unlikely to be met.

“The new Transport Minister was made aware of the emerging EGIP cost and programme on May 24th 2016 following his official appointment.

“The minister was not prepared to simply accept this and challenged Network Rail to revisit their analysis.”

The Sunday Post asked what date in early May news of the delay was passed on and was told officials were “fairly certain” it was May 4 – the day before the Holyrood election.